1. Field of the Invention
This invention relates to an image forming method and an electrophotographic apparatus using the image forming method.
2. Description of the Related Art
As an electrophotographic photosensitive member, in view of advantages of low prices and high productivity, an organic electrophotographic photosensitive member has become popular, which has a support and a photosensitive layer (organic photosensitive layer) provided thereon using an organic material as a photoconductive material (such as a charge generating material and a charge transporting material). As the organic electrophotographic photosensitive member, in view of advantages such as a high sensitivity and a possibility of designing various materials, an electrophotographic photosensitive member is prevalent which has a multi-layer type photosensitive layer including a charge generation layer containing a charge generating material such as a photoconductive dye or a photoconductive pigment, and a charge transport layer containing a charge transporting material such as a photoconductive polymer or a photoconductive low-molecular weight compound, with the layers being superposed one on the other.
To the surface of the electrophotographic photosensitive member, electrical external force and/or mechanical external force is/are applied during charging, exposure, development, transfer and cleaning, and hence the electrophotographic photosensitive member is also required to have durability to such external force. Specifically, the photosensitive member is required to have durability to scratching and wear of its surface due to such external force, i.e., scratch resistance and wear resistance.
As for a technique for improving the scratch resistance and wear resistance of the surface of the electrophotographic photosensitive member, an electrophotographic photosensitive member is disclosed which has as a surface layer a cured layer using a curable resin for a binder resin (see Japanese Patent Application Laid-Open No. H02-127652).
An electrophotographic photosensitive member is also disclosed which has as a surface layer a charge transporting cured layer formed by curing-polymerizing a monomer having a carbon-carbon double bond and a charge transporting monomer having a carbon-carbon double bond by heat or light energy (see Japanese Patent Applications Laid-open No. H05-216249 and No. H07-072640).
An electrophotographic photosensitive member is further disclosed which has as a surface layer a charge transporting cured layer formed by cure-polymerizing a hole transporting compound having a chain-polymerizable functional group in the same molecule by energy of electron rays (see Japanese Patent Applications Laid-Open No. 2000-066424 and No. 2000-066425).
Thus, in recent years, as a technique by which the scratch resistance and wear resistance of the peripheral surfaces of organic electrophotographic photosensitive members are improved, a technique has been established in which the surface layers of electrophotographic photosensitive members are composed of cured layers so as to improve the mechanical strength of the surface layers.
The electrophotographic photosensitive member is commonly used in an electrophotographic image forming process having, as mentioned above, a charging step, an exposure step, a developing step, a transfer step and a cleaning step. In the electrophotographic image forming process, the cleaning step of removing transfer residual toner remaining on the electrophotographic photosensitive member after the transfer step to clean the peripheral surface of the electrophotographic photosensitive member, is important in order to obtain sharp images.
As a cleaning method, in view of advantages such as low costs and easiness of designing, a method is prevalent in which a cleaning blade is brought into contact with the electrophotographic photosensitive member surface to delete the gap between the cleaning blade and the electrophotographic photosensitive member so that a toner can be prevented from escaping to thereby scrape the transfer residual toner off.
However, in the cleaning method using a cleaning blade, the frictional force between the cleaning blade and the electrophotographic photosensitive member is so large that chattering and turn-up of the cleaning blade are liable to occur and the blade edge tends to be gouged or chipped off to cause faulty cleaning. The chattering of the cleaning blade is a phenomenon in which the frictional resistance between the cleaning blade and the peripheral surface of the electrophotographic photosensitive member becomes high and vibrates the cleaning blade. The turn-up of the cleaning blade is a phenomenon in which the cleaning blade becomes reversed in the direction of surface movement of the electrophotographic photosensitive member.
These problems concerning the cleaning blade become more remarkable as the surface layer of the electrophotographic photosensitive member has higher mechanical strength, i.e., as the peripheral surface of the electrophotographic photosensitive member is more difficult to abrade.
In addition, the surface layer of the organic electrophotographic photosensitive member is commonly often formed by dip coating, and the surface of a surface layer formed by dip coating is so smooth that the cleaning blade and the peripheral surface of the electrophotographic photosensitive member come into contact with each other in a larger area and the frictional resistance between the cleaning blade and the peripheral surface of the electrophotographic photosensitive member increases. Thus, the above problems become remarkable.
As one of methods for overcoming the chattering and turn-up of the cleaning blade, a method is known in which the surface of the electrophotographic photosensitive member is appropriately roughened. As techniques for roughening the surface of the electrophotographic photosensitive member, the following are disclosed, for example.
A technique in which the surface roughness (roughness of peripheral surface) of the electrophotographic photosensitive member is controlled within a specific range in order to make transfer materials readily separable from the surface of the electrophotographic photosensitive member, and a method in which drying conditions for forming a surface layer are controlled to roughen the surface of the electrophotographic photosensitive member in an orange peel state (see Japanese Patent Application Laid-open No. S53-092133); a technique in which the surface layer is incorporated with particles to roughen the surface of the electrophotographic photosensitive member (see Japanese Patent Application Laid-open No. S52-026226); a technique in which the surface of a surface layer is polished with a wire brush made of a metal, to roughen the surface of the electrophotographic photosensitive member (see Japanese Patent Application Laid-open No. S57-094772); a technique in which the surface of the organic electrophotographic photosensitive member is roughened in order to solve turn-up of the cleaning blade and chipping of the edge portion which are problems occurring in the case where a specific cleaning means and toner are used in an electrophotographic apparatus whose process speed is higher than a specific process speed (see Japanese Patent Application Laid-open No. H01-099060; a technique in which the surface of a surface layer is polished with a filmy abrasive to roughen the surface of the electrophotographic photosensitive member (see Japanese Patent Application Laid-open No. H02-139566); and a technique in which blasting is carried out to roughen the peripheral surface of the electrophotographic photosensitive member (see Japanese Patent Application Laid-open No. H02-150850).
However, these have no specific disclosure as to details of surface profiles of the electrophotographic photosensitive members thus surface-roughened.
From the viewpoint of roughening surface layers appropriately, the roughening of surfaces by the above conventional techniques can be seen to bring about certain effects in reducing frictional force with the cleaning blade. However, a further improvement is being sought. A further improvement is being sought in order to solve the problems on how to control cleaning performance and prevent toner adhesion from a microscopic viewpoint, in the respect that the surface profile is streaky or is in indefinite form or has unevenness with a difference in size.
Based on detailed analyses and studies made taking note of the controlling of a surface profile of the electrophotographic photosensitive member, an electrophotographic photosensitive member having certain dimples has been proposed (see Japanese Patent Application Laid-open No. 2001-066814). This method has hit a directionality in which the problems such as cleaning performance and electrostatic memory of electrophotographic photosensitive member caused by rubbing may be solved, but a further improvement in performance is being sought.
A technique is also disclosed in which the surface of the electrophotographic photosensitive member is processed by compression forming by means of a stamper having unevenness in the form of wells (see WO2005-093518). As compared with the techniques disclosed in the above patent documents, this technique is considered to be more effective in solving the above problems in the respect that an unevenness profile with independent shapes can be formed on the electrophotographic photosensitive member surface with good controllability. According to this method, it has been reported that an unevenness profile in the form of wells each having a length or pitch of from 10 to 3,000 nm is formed on the surface of the electrophotographic photosensitive member, and releasability of toner is improved and nip pressure of the cleaning blade can be reduced, consequently enabling abrasion of the photosensitive member to be reduced.
However, in the image forming method in which the nip pressure of the cleaning blade has been thus reduced, faulty cleaning tends to occur in an environment of low temperature and low humidity. In addition, in the image forming method using a photosensitive member having such an unevenness surface profile, at the time of outputting a high-MTF chart in a case where, e.g., one line/one space images are formed at 600 dpi, the toner is liable to be trapped in depressed portions on the photosensitive member surface when passing through a developing nip, even at positions having low latent image charge density, tending to lower line reproducibility.
As discussed above, according to the conventional techniques, certain effects can be achieved on improvement in running performance, improvement in cleaning performance and prevention of image defects. However, under existing circumstances, there remains room to further improve overall performance.